The invention relates generally to communication systems, and more specifically, to handoff techniques in a communication network.
A wireless communication network may include devices capable of communicating wirelessly. The network may include network nodes, and one or more devices may communicate with each network node to access the communication network. For example, a wireless device may communicate with the network node capable of providing the best signal strength, which may be the network node closest to the location of the device. As a wireless device changes location (e.g., a mobile phone user may take the phone from one end of a city to another), the network node capable of providing the best signal strength may also change. Thus, a wireless device communicating with one node may experience a “handoff” as a portion of the path of the communication (e.g., the call, data session, etc.) is transferred from one network node to another. Handoffs which occur between like network nodes, referred to as “horizontal handoffs,” may occur substantially seamlessly. For example, when a communication path between a mobile phone and one base station is transferred to another base station, the horizontal handoff may occur with little delay, such that packet loss is undetected by the user.
As wireless communication systems have evolved, the number of different link layer technologies in a communication network has increased, potentially complicating the handoff process between a wireless device and a network node. A wireless communication system may include network nodes having different access technologies, such as base stations and access points, to connect different wireless devices, such as mobile phones, laptops, personal digital assistants, etc., to the wireless communication network. In such a heterogeneous wireless communication network, different wireless devices may also communicate with different network nodes, which may have different link layer technologies. For example, a mobile phone may communicate with one or more different base stations or access points, depending on the signal strength in a particular communication path. Such transfers of communication between different types of network nodes (e.g., from a base station to an access point) may be referred to as a “vertical handoff.” However, vertical handoffs may have increased delays (compared to the relatively seamless horizontal handoff), and inefficient vertical handoffs may result in packet loss, or terminated communications. For example, some delays may result from oscillating vertical handoffs, commonly referred to as the “ping pong” effect. Thus, a method of managing vertical handoffs may improve communication quality in a wireless communication network.